| The assessment of complex mixtures of environmental contaminants and their effects on marine biota requires attention from the scientific community. 5-Fluorouracil is a cytostatic group 3 anti-cancer drug (not classifiable as to its carcinogenicity to humans, IARC) used in treatment for colon, pancreatic and breast cancer among others. In surface waters, 5FU has been predicted to be within the 5-160 ng/L range. In the presence of other contaminants, this pharmaceutical compound can interact and form mixtures of contaminants, such as adhering to plastics and interacting with metal nanoparticles. This study aimed to comprehend the effects of 5-Fluorouracil (5FU; 10 ng/L) alone and mixed with two emerging contaminants (Mix) namely: silver nanoparticles (nAg; 20 nm; 10 μg/L) and polystyrene nanoparticles (nPS; 50 nm; 10 μg/L), in an in vivo (21 days) exposure of the marine mussel Mytilus galloprovincialis. A multibiomarker approach namely the antioxidant defence system (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPx), glutathione – S – transferases (GST) activities), and oxidative damage (LPO) were the chosen biomarkers analysed in gills and digestive gland of mussels. In gills of mussels, after exposure to 5FU, SOD and CAT activities increased significantly along the course of time, whilst GPx activity was activated on the 21st day. On the other hand, GST activity was inhibited in the gills after 3 days of exposure. In mussels exposed to Mix, the antioxidant enzymes activity increased significantly in the gills after 3 days, maintaining high activity until the 14th day of exposure. GST activity, on the contrary, is inhibited after 3 days and activated on the 14th day of exposure. In the digestive gland, 5FU also led to a significant increase in SOD and CAT activity after 3 days, however a decrease pattern is observed on the remaining exposure days. GPx activity in digestive gland shows a similar pattern as the activity measured in gills, and GST activity is inhibited after 14 days. Following exposure to Mix, SOD and GPx activity increased significantly after 3 days, whilst CAT activity decreased significantly after 7 days, and GST activity increased after 21 days. Moreover, no significant oxidative damage was encountered in either tissue after exposure to 5FU. However, Mix-exposed LPO levels increased in the gills after 3 days and decreased at 21 days, whereas in the digestive gland, an increase in LPO levels by 3.6-fold occurs on the 7th day, followed by a decrease after 21 days. Mussels were able to defend themselves from toxicity of 5FU, however not the same was found in Mix-exposed mussels. Therefore, mixtures of emerging contaminants are of incrementing concern, and more ecotoxicological studies should be carried out to evaluate the potential impacts of these mixtures. |